Supercharger installations are one way of improving the filling of cylinders with combustion air in internal combustion engines. Such installations can be implemented as exhaust-gas turbochargers or mechanically driven superchargers or pressure wave superchargers, and they increase the pressure level in the intake tract of an internal combustion engine in order to increase the filling efficiency of the cylinders when the engine's intake valves are open. In the case of exhaust-gas turbochargers, the so-called “turbo hole” occurs when the engine is operating at low speeds, since because of the lower volume flow of exhaust gas, the mechanical power delivered to the compressor impeller of the turbocharger by the turbine wheel is not sufficient to increase the pressure in the intake tract of the engine.
With exhaust-gas turbochargers, which are used on both auto-ignition and external-ignition type engines, the above-mentioned turbo hole occurs in the lower speed range of the engine. When an engine is in this operating mode, the volume flow of the exhaust gas generated by the engine is not sufficient to drive the compressor impeller of the exhaust-gas turbocharger at a rotation speed that can be utilized to increase the pressure adequately in the engine's intake tract.
One way of coping with the above-described characteristic operating feature of exhaust-gas turbochargers is to provide the exhaust-gas turbocharger with booster units—electrically drivable, for example—which can be switched on, for example via an overrunning clutch, when the engine reaches a given lower speed, and can be cut out, for example via an overrunning or overriding clutch or the like, once a given engine speed that prevents turbo hole has been exceeded.
Impulse turbochargers are known from the prior art. They are disposed in the intake tract of an internal combustion engine, on the intake side of the engine. The impulse turbochargers used heretofore operate on the butterfly valve principle, and have a butterfly-valve-like mechanism integrated into the engine's charge air supply system. However, the butterfly valve principle used has the major disadvantage that the stability of the butterfly valves is consistently unsatisfactory, due to the extremely short switching times and the frequent mechanical contact with stop faces. The frequent striking of driven butterfly valves of such impulse turbochargers against the walls of the charge air supply conduit is accompanied by mechanical wear and causes not-insignificant noise generation in the intake tract. In addition, the wear to which the valves of the impulse turbochargers used are subjected with increased engine operating time causes the valves to be no longer completely tight when closed, and an ever-increasing leakage flow of the charge air begins to occur along the no longer tightly closing valves and has a negative impact on the efficiency of an impulse turbocharger of this design in the intake tract of an internal combustion engine.
If the impulse turbocharger used in the intake tract of an internal combustion engine is configured as a rotary slide valve (for example in the form of a transversely drilled cylinder), the design volume of the impulse turbocharger has to be relatively large in order to cover the entire opening cross section of the charge air supply conduit. In addition to the large spatial requirements of impulse turbochargers configured in this manner, they also have the disadvantage of large moving masses, causing their use to place heavy demands on the drive and elicit high mass moments of inertia. Short switching times are difficult to achieve with impulse turbochargers implemented as rotary slide valves.
With auto-ignition engines and any type of engine that has an exhaust-gas return valve, there is a further exacerbating disadvantage in the form of a deposit problem caused by the exhaust-gas return valve. Coatings of tar several millimeters thick must be kept under control throughout the portion of the intake manifold impinged on by the exhaust gas. An increase in mass caused by the layers of tar deposited on the side walls of that portion of the intake manifold results in major problems with switching times. In addition, the butterfly valves of an impulse turbocharger operating on the butterfly valve principle may stick, ultimately causing the supercharger unit to fail. Throttle devices are usually installed in the intake tract to achieve load control and filling control in the engine's part-load range.